Glycosides of 6-mercaptopurine



United States Patent Ofiice 3,974,929 Patented Jan. 22, 1983 New York Fiied Dec. 23, 1958, Ser. No. 782,410

No Drawing. Claims priority, application Great Britain Aug. 11, 1955 6 Claims. (Cl.

The present invention relates to 9-glycosido-6-mercaptopurines and to a process for preparing the same.

The ability of 6 mercap-topurine to interfere with cell division has found a useful expression in the production of remissions of acute leukemia. The mechanism of action of G-mercaptopuriue is believed to be as an autagonist of the natural 6-substituted purines, which exist in cellular compositions combined through glycoside linkages.

The biological activity of 6 mercaptopurine is modified, and becomes more selective in the new compounds with the result that the range of usefulness of the growth inhibitor is extended.

The usual method of preparing purine glycosides is by the reaction of a heavy metal salt of the purine with a glycosyl halide. In the present instance this method is inoperable presumably because the metal salts are attached to the sulfur of the mercaptan group. However, it has been found that o-benzylmercaptopurine will form a suitable silver salt, and that debenzylation of the eventual 9-glycosido-6-benzylmercaptopurines can be effected by treating with sodium in liquid ammonia.

The above method was disclosed in our co-pending application Serial No. 574,575, now abandoned, of which the present is a continuation-in-part. In that application, there was also described an alternative method wherein 6-chloropurine was converted through its chloromercuri derivative to its 9-triacetylriboside and that, in turn, by reaction with thiourea and subsequent deacetylation resulted in thioinosine.

This second route has now been enlarged by two variations. It has been found that the 6-chloropurines are converted to 6-mercaptopurines with especial convenience by reaction with thio-acetic acid. Presumably a 6-thioacetate is formed first and this undergoes spontaneous hydrolysis to the 6-thiol.

The synthesis from simple purine and sugar moieties of nucleosides is time consuming and the yields are inferior. Our second variation consists of starting with the naturally occurring and reasonably available nucleosides, inosine and guanosine. The first step is to protect the sugar hydroxyls by acetylation or benzoylation. At this point (II in the chart) a direct thiation is possible but results in excessive tar-formation. We have found that it is more satisfactory to treat the acylated nucleoside with phosphorus oxychloride in the presence of a weak base and so to obtain the 6-chloronucleoside (ill) which can then be converted to the -mercap-tonucleoside (V), by the methods previously discussed. Practical success of either route is in fact rather surprising since these nucleosides are very sensitive, especially to acids and alkalines. It is not apparent why phosphorus oxychloride should be less damaging than phosphorus pentasulfide, but this appears to be the case.

Not only the nucleosides of 6-mercaptopurine and thioguanine but also their acylated derivatives (IV) are of therapeutic interest. Esterification of the sugar hydroxyls modifies the solubility characteristics of the compounds. It is probable that the ester moieties are removed in the body but the absorption of the drug and also its rate of excretion being modified, the action may be favorably affected.

6-Benzylmercaptopurine Silver 10 gm. of 6-benzylmercaptopurine is dissolved in 200 cc. concentrated NH OH. This process is endothermic and the mixture should be kept warm on the steam bath until the solid has dissolved. A solution of 7.2 gm. of silver nitrate is added to the ammoniacal solution of the purine with vigorous stirring. A heavy white gelatinous precipitate forms at once. The viscous solution is diluted with 300 cc. of water and left on the stirrer for one hour. The precipitate is then removed by filtration and Washed repeatedly with water. Yield 13.2 gm. (92% of theory), M.P. 240-244 dec.

6-Benzylmercapto-9-{3-d-Tetraacetylglucopyranosylpurine 5.07 gm. (0.0145 M) of the above compound was carefully dried and suspended in cc. anhydrous Xylene. To the suspension was added an equivalent (5.4 gm.) of tetraacetyl-a-d-glucopyranosyl chloride. The suspension was allowed to reflux for 17 hours with stirring. The gray precipitate was removed by filtration and washed with chloroform and the xylene filtrate was decolorized with charcoal and concentrated in vacuo on steam bath to remove all xylene. The amber viscous syrup was dissolved in methanol from which the acetylated nucieoside precipitates on standing in the cold. The precipitate was washed with anhydrous ether. It melts at 9499 (hydrate?) and resolidifies, remelting at 3 EXAMPLE 2 0.5 g. of the above compound was dissolved in 25 cc. of saturated ethanolic ammonia and allowed to stand at room temperature for 43 hours. The solution was concentrated to dryness, dissolved in cc. of absolute ethanol and left to crystallize overnight in the cold. The product was filtered. and washed with ether-ethanol 3:1. MP. 110.

Q-B-d-Glucopyranosy 1-6 -M ercap topuriize 0.5 gm. of the above was dissolved in 100 cc. liquid Nil-l Bits of metallic sodium were added until the first permanent blue color. The color was then discharged by adding solid NH Cl.

The ammonia was allowed to evaporate. The last traces were removed by warming the reaction flask in vacuo. A solution of cc. absolute alcohol containing 0.5 cc. glacial acetic acid was added to the residue. A crystalline product was obtained from the solution; M.P., 205. A max. pH 1, 223, 322 my; pH 11, 310.

EXAM'PLE 3 6-Belzzylmercapto-9-( B-d-Z ,5-Diacetylglucofuranuranolactonyl Purine 5.5 gm. (0.0157 M) of o-benzylmercaptopurine silver and an equivalent (4.4 gm.) of 1-chloro-2,5-diacetylglucuronolactone were suspended in 150 cc. of anhydrous xylene. The mixture was refluxed for 17 hours with stirring, and was then filtered to remove the AgCl. The filtrate was decolorized with charcoal and concentrated to a syrup in vacuo. The syrup was dissolved in 10 cc. of absolute ethanol. On standing for 26 hours at 5, a yellowish crystalline precipitate formed. Yield 1.3 gm. (17% of theory).

The ultraviolet absorption spectrum of this was almost identical with that of 9-riboiuranosyl-6-benzylmercaptopurine, thus confirming the ascribed structure. A max. pH 1, 295 Ill/L; pH 11, 293 ma. min pH 1, 253 mu; pH 11, 253 m 6 mol pH 1, 16.3; pH 11, 16.6. This property is especially notable with 9-riho-furanosyl-6- mercaptopurine, which most closely resembles the naturally occurring nucleosides.

EXAMPLE 4 The Synthesis of Q-Ribofamncsyl-o-Mercaptopurine 10 g. of 6-beuzylmercaptopurine-silver was added to a solution of 6.5 g. of 1-chloro-2,3,5-triacetyl riboiuranose in 696 ml. anhydrous Xylene. The mixture was refluxed with stirring for 48 hours. The residue of AgCl and unreacted silver alt was removed by filtration and the decolorized filtrate concentrated to a syrup in vacuo. The product 9-(2,3,5'-triacetylribofuranosyl)-6-benzylrnercaptopurine did not crystallize, out showed the expected ultraviolet absorption spectrum with max. at 2 mu, 13H 1 (O 11.

9-Kibofuralzosyl-6-Be/zzylmei'capropzirine The berszylmercaptonucleoside was prepared from the acetylated derivative above by dissolving the latter in 50 ml. absolute ethanol saturated with NH After standing overnight at room temperature, the solution was concentrated to a syrup in vacuo. No crystals were obtained, but the ultraviolet absorption spectrum was in agreement with that previously obtained for the corresponding 9-glucosyl derivative. i. mm. 290 m pH 1 to 11.

Q-Ribofaranosyl-d-Blercaptopnrine This nucleoside of S-mercaptopurine was obtained upon debenzylation of the syrup produced above. 2 g. of the benzylrnercapto derivative was dissolved in 56 ml. li uid EH to which was added 0.4- g. metallic Na. After evaporation of the NH and dissolving the residue in 10 ml. 95% ethanol, 1 ml. acetic acid was added,

EXAMPLE 5 Chloromercuri-d-Chloropurine (II) 28.8 g. of 6-chloropurine was dissolved in 200 m1. of water containing 7.4 g. NaO H. A solution containing 50.5 g. HgCl in 250 ml. ethanol was added. 51 g. of (II) was obtained.

9-(2',3,5-Triace:ylribofuraiwsyl) -6-Chl0ropurine (HI Eight g. of chloromercuri-6-chloropurine was added to a solution of 7 g. l-chloro-2,3,5-triacetylribofuranose in ml. anhydrous Xylene. The solution was refluxed for 48 hours, filtered and the filtrate was concentrated to a syrup. The product was an impure oil.

Two g. of the syrup (III) was refluxed with 0.2 g. thiourea and 0.2 g. sodium acetate in absolute ethanol for 18 hours. The resulting solution of the thiouronium salt (IV) was filtered, treated with H 3 to remove any remaining Hg, decolorized with Darco, concentrated to a syrup and taken up in absolute ethanol. The ethanolic solution was saturated with NH and left for 18 hours at room temperature. A very small amount (50 mg.) of product was obtained.

A max.=225, 321 at pH 1; 234, 311 mp. at pH 11; the product gives a positive Mohlisch test and was shown by paper chromatography to have a mobility resembling that of the corresponding glucosyl derivative.

EXAMPLE 6 6'-Hydr0xy-9-(2,3,5-Tri-0-Acetylribofumnosyl) -Purine (Ilac) 15 g. of inosine (I) is suspended in 200 ml. pyridine. T o the suspension is added 100 ml. acetic anhydride. After stirring until homogeneous, the mixture is kept on the steam bath for 2 hours. The resulting clear amber-colored solution is concentrated to semi-solid state in vacuo. 250 ml. of ice water is added to the residue, whereupon the solid dissolves with the evolution of heat. Upon cooling for 5 minutes in an ice bath, the white crystalline product appears. After keeping at 4 C. for one hour, the crystals are collected by filtration and washed with ice water. Yield, 19.5 g. (89% of theory). M.P. 230. A max.=245m (in absolute EtOH).

EXAMPLE 7 6-Chl0r0-9-(2,3,5-Tri-0-A cetylribofuranosyl) -Purine (Illac) 16.0 g. of triacetylinosine (II) is intimately mixed with 10 ml. of dimethylaniline. To the mixture is added 100 ml. of POCl The suspension is heated on the steam 'bath for 4 hours (anhydrous conditions). The homogeneous dark brown solution is then concentrated in vacuo on the steam bath to remove the excess POCI The remaining brown syrup is dissolved in 250 ml. CHC13. The CHCl solution is washed 5 times with 75 ml. pertions of H in a separatory funnel, after which the water washings are at pH to 6. The CHCl layer is dried over anhydrous Na SO and is concentrated to a syrup. Final traces of solvent are removed under high vacuum. The yield of crude product isolated as a syrup is 14.8 g. (89% of theory. A max.=265 m (in H O).

EXAMPLE 8 6-Mercapt0-9-(2,3,5-Tri-O-Acetylribofuranosyl) -Purine (l Vac) 1.3 g. of (III) was dissolved in ml. of absolute ethanol. To this solution was added a solution containing 0.6 g. of sodium thioacetate in 10 ml. of absolute ethanol. The clear solution was refluxed on the steam bath for 1 hour. The warm solution was filtered, and, upon cooling, the product crystallized in the form of white plates. Yield, 800 mg. (62% of theory). A max.:325 na in absolute ethanol.

EXAMPLE 9 6-Mercapr'o-9-Ribofuranosylpurine (Va) 95 mg. of (IV) was dissolved in 25 ml. of absolute ethanol saturated with NH The solution was kept at room temperature for 18 hours after which it was concentrated in vacuo to about 5 ml. and cooled in an ice bath. 40 mg. of pure 6-MP riboside (Va) was isolated; (60% of theory). A max.=225, 321 at pH 1; 234, 31111111. at pH 11.

EXAMPLE 10 6-H ydr0xy-9-(2,3 ,5 -Tri-O-Benzoylribofuranosyl -Purin'e (Had) Five g. of inosine was suspended in 10 ml. of pyridine. The mixture was cooled at 0 in an ice bath. To the cold suspension, 25 ml. of CHCl followed by 10 g. of benzoyl chloride was added. The mixture was heated at 100 for 2 hours, allowing the CHCl to distill off.

The resultant syrup was dissolved in 100 ml. of CHClg- The CHCl solution was washed with saturated NaHCO solution and then with saturated Natl-180 solution foilowed by water. After drying over NH2SQ4 the CHCl solution was concentrated in vacuo to a syrup which, on treatment with anhydrous ether, formed the solid benzoyl derivative. Yield, 10 g. (92% of theory) N=9.61% Theory N=9.68%. A max.=230 and 265 my. in alcohol.

EXAMPLE 11 Five g. of tribenzoylinosine (Example 10) was suspended in 5 ml. of dimethylaniline. To this suspension was added 61 g. of P001 whereupon the solid dissolved. The mixture was heated at for 4 hours. The resulting light yellow solution was poured into 800 m1. of ice water- CHCl- (1:1 by volume). The water layer was extracted twice with CHCl The CHCl layer was Washed twice with saturated N-aHCO solution and then with water. After drying over Na SO the CHClg layer was concentrated in vacuo to a syrup. The resulting syrup was dissolved in 100 ml. of absolute alcohol and poured into 600 ml. of water. Upon acidification to pH 2 with HCl, a precipitate was formed. Yield 6 g. of crude product. A max.=230 and 260 m in alcohol. The 230 mp. peak is characteristic of the benzoyl derivatives while the 260 peak is similar to that of the parent purine, 6-chloropurine with a peak at 265 (aqueous solution, pH 1). The product contains Cl (organic) and gives a positive Mohlisch test.

EXAMPLE 12 6-Mercapt0-9-(2,3,5-Tri-0-Benz0ylribofuranosyD-Purine (I Vad One g. of the 6-chloronucleoside of Example 11 was dissolved in 25 ml. of absolute alcohol. To this was added a solution containing 0.4 g. of sodium thioacetate in 5 m1. of alcohol. The mixture was heated under reflux for one hour. On cooling for 18 hours at 4 C., a flocculant precipitate was formed. The solution was acidified with 0.1 N HCl and filtered. Yield, 400 mg. N=9.35%; theory, N=9.42%. A max.=230, 265 and 322 111 1. in abs. alcohol.

EXAMPLE 13 Z-Amino-d-Hydroxy-Q(2,3,5-Tri-O-Acetylribofuranosyl) Purine ([1110) Fifty g. of guanosine (commercial grade) was suspended in 500 ml. of pyridine. To this was added 250 ml. of acetic anhydride. The mixture was heated at 100 for 17 hours. The resulting solution was poured into 1600 ml. of water and extracted with CHCl (3-200 ml. portions). The CHCl solution was washed twice with saturated NaI-ISO solution (2 x 200 ml.), twice with 200 ml. portions of H 0, dried over Na SO and concentrated to a syrup in vacuo. The syrup, on trituration with anhydrous ether formed a crude solid product (63 g.) A max. 258 m at pH 6; 265 mp. at pH 12. The product shows U.V. characteristics similar to guanosine as would be expected.

EXAMPLE 14 2-Amin0-6-Chl0ro-9-(2,3,5-Tri-O-Acetylribofuranosyl)- Purine (IIIbc) Twenty-five g. of the above ester was suspended in 35 ml. of dimethylaniline. To this was added 240 g. of POCl The mixture was heated at 100 under reflux for 4 hours. The resulting solution was concentrated in vacuo on the steam bath to a syrup. The syrup was dissolved in 200 ml. of CHcl which solution was extracted several times with 75 ml. portions of H 0 until the pH of the washings was about 4. After drying over Na- SO the CHCl layer was concentrated in vacuo to a syrup. To this was added anhydrous ether. The resulting hygroscopic solid was dried in vacuo. Yield 12 g. A max. 252 and 285 m in alcohol. Contains chlorine (organic). Positive Mohlisch test.

Z EXAMPLE 15 Z-Amino-dJifetca12ta-9- (2,3,5-Tri-Q-A ceiyiribofurano- 5y!) -Pnrine (ii be) One g. of the above chloro compound Was dissolved in 25 ml. of absolute alcohol. To this was added a solution of 0.5 g. of sodium thioacetate in 5 ml. of absolute alcohol. The mixture was refluxed for 2 hours, filtered, and concentrated to dryness in vacuo. The solid residue was treated with 50 ml. of water. A precipitate formed with UV. characteristics similar to the parent purine compound, thioguanine. U.V., 7\ max. at 250 and 340 Inn in absolute alcohol. The 340 peak is characteristic of the mercapto group of thioguanine. A positive Mohlisch test indicates the presence intact of the ribosyl group.

EXAMPLE 16 Tribeizzoyl Gzmnosine (Hbd) Benzoylation was accomplished by the method described for the benzoylation of insosine (Example 10). The product was isolated as a crystalline solid, Ml. 205 8. N=11.36%. Calculated N=11.75%. Amara: 230, 270 in alcohol.

EXAMPLE l7 2-Amino-6-C1'zl0r0-9-(2,3,5-Tri-O-Benzoylribofuranosyl)- Purine (lllbd) Five g. of tribenzoylinosine (Example 16) was chlorinated with POCi as described in Examples 11 and 14. The product was isolated as an amorphous powder, probably a salt of H P0 It contains chlorine (organic), N, and P. Analysis for N: Found, N=9.57%; calculated for 1 mole H PO N=9.85%. A max.=23), 280 mp. in alcohol.

One-tenth g. or" Z-amino-6-mercapto-9-triacetylrihofuranosylpurine (Example 15) was dissolved in 2.5 cc. of alcohol saturated with ammonia. The solution was allowed to stand over-night at room temperature and wherein R is selected from the class consisting of NH:

and hydrogen, R is selected from the class consisting of CHZOII, and hydrogen, R" is selected from the class consisting of COCH COC H and hydrogen and n is an integer having the values 2 and 3.

2. A 9-d-glucoside of G-mercaptopurine. 3. A 9-d-riboside of -mercaptopurine. 4. A 9-d-riboside of 2-amino-6-mercaptopurine. 5. A Q-acetylated glucuronicle of -mercaptopurine. 6. A 9-glycosido-6-mercaptopurine.

Reterences Cited in the file of this patent UNITED STATES PATENTS Baker Sept. 16. 1958 Goldman et al Sept. 16., 1958 OTHER REFERENCES 40 Friedkin, Biochim et Biophys Acta. 18, 447-448 (November 1955), cited in Chemical Abstracts. 50, 3516 (1956). (Chemical Abstract available in PD. Sci. Lib.)

Johnson, 31:, et al., I. Am. Chem. Soc. 78, 3863 (1956). (Copy in P.O. Sci. Lib.) 

1. A COMPOUND REPRESENTED BY THE FORMULA 